Rooting capacity of Pelargonium cuttings with special regard to carbohydrate availability and photosynthetic performance [Elektronische Ressource] / von Vijaya Kumar Rapaka

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Rooting capacity of Pelargonium cuttings with special regard to carbohydrate availability and photosynthetic performance Vom Fachbereich Gartenbau der Universität Hannover zur Erlangung des Grades eines DOKTORS DER GARTENBAUWISSENSCHAFTEN -Dr. rer. hort.- genehmigte Dissertation Von MSc (Ag.) Vijaya Kumar Rapaka geboren am 1. August 1976 in Narsapur, Indien 2004 Chairman: Prof. Dr. B. Beßler Co-Chairman: Prof. Dr. M. Schenk an: Dr. U. Druege Day of promotion: 08 January 2004 Mom and Dad – for you. Abstract Rapaka, V.K. Rooting capacity of Pelargonium cuttings with special regard to carbohydrate availability and photosynthetic performance This study investigated the relationship between carbohydrate availability and adventitious root formation of two cultivars (‘Isabell’ and ‘Mitzou’) of Pelargonium x hortorum cuttings, when affected by season of stock plant cultivation, stock plant age, cutting cold-storage (variable temperature regime for 4 days), as well as sustenance of current photosynthesis of those cuttings as additionally affected by rooting environment [greenhouse -2 -1(GH); climate chamber (CC): PPFD 100 µmol m s , relatively low light].

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Rooting capacity of Pelargonium cuttings with special regard to
carbohydrate availability and photosynthetic performance





Vom Fachbereich Gartenbau
der Universität Hannover
zur Erlangung des Grades eines



DOKTORS DER GARTENBAUWISSENSCHAFTEN
-Dr. rer. hort.-



genehmigte Dissertation




Von
MSc (Ag.) Vijaya Kumar Rapaka
geboren am 1. August 1976 in Narsapur, Indien

2004































Chairman: Prof. Dr. B. Beßler
Co-Chairman: Prof. Dr. M. Schenk an: Dr. U. Druege
Day of promotion: 08 January 2004
































Mom and Dad – for you.
Abstract
Rapaka, V.K.
Rooting capacity of Pelargonium cuttings with special regard to carbohydrate
availability and photosynthetic performance
This study investigated the relationship between carbohydrate availability and
adventitious root formation of two cultivars (‘Isabell’ and ‘Mitzou’) of Pelargonium x
hortorum cuttings, when affected by season of stock plant cultivation, stock plant age, cutting
cold-storage (variable temperature regime for 4 days), as well as sustenance of current
photosynthesis of those cuttings as additionally affected by rooting environment [greenhouse
-2 -1(GH); climate chamber (CC): PPFD 100 µmol m s , relatively low light]. Carbohydrate
distribution, chlorophyll fluorescence parameters, chlorophyll quality and quantity, and net
photosynthetic rates of the cuttings were analyzed during propagation.
Leaf carbohydrate levels of the cuttings were less influenced by season at harvest, but
were significantly decreased after cold-storage. Starch, in particular, reduced to trace amounts
as early as 1 day after cold-storage. Basal stem carbohydrate levels at harvest were higher in
summer when compared to those in spring and winter, which was predominantly due to
higher starch. Cold-storage significantly reduced the basal stem carbohydrates only in spring
and winter. Pre-insertion non-photochemical quenching (qN) of chlorophyll fluorescence was
less influenced by season but significantly decreased by cold-storage. However, during the
subsequent course of propagation, there were no significant differences between unstored and
stored cuttings for both qN (measured at day 1, 4, 7 & 14) and carbohydrate levels (at day 7)
in any specific rooting environment, except in GH during winter for basal stem carbohydrates.
Furthermore, the cuttings propagated in CC had significantly lower qN and carbohydrate
levels when compared to those in GH during spring and summer. This appears to be a
reflection of lower current photosynthetic performance, and consequently, lower production
and basipetal transport of carbohydrates in the high light adapted cuttings propagated under
relatively low light (CC). The carbohydrate distribution between the leaves and the basal stem
during the rooting period indicates, that the newly assimilated carbon was predominantly
partitioned between sucrose and starch in leaves, subsequently exported basipetally towards
the basal stem, and there was mostly accumulated in sugar pools.
Highly significant positive correlations were found between both leaf sucrose levels
and qN at insertion and root number when unstored and stored cuttings of ‘Isabell’ were
propagated in CC (relatively low light) irrespective of the season. In GH, however, they were
only correlated in winter (low light intensity). Thus, pre-insertion qN may be used as a rapid
and non-destructive physiochemical index for assessing the rooting efficiency of the cuttings
when propagated under defined relatively low light conditions. Mean leaf sucrose (day0 +
day7) explained the whole variation in root number caused by three contrasting seasons, stock
plant age, cold-storage, and rooting environment. Results indicate that even when basal stem
carbohydrate levels are high at insertion, adventitious root formation of the cuttings is
predominantly influenced by basipetal translocation of carbohydrates during propagation,
derived from both pre-insertion leaf carbohydrate reserves and current photosynthesis, the
latter of which is itself substantially affected by rooting environment. Zusammenfassung
Rapaka, V.K.
Bewurzelungsfähigkeit von Pelargonium-Stecklingen unter besonderer Betrachtung der
Kohlenhydratverfügbarkeit und der Photosyntheseleistung

Diese Studie untersuchte die Beziehung zwischen Kohlenhydratverfügbarkeit und
Adventivwurzelbildung zweier Genotypen (cv. „Isabell“ und cv. „Mitzou“) von Pelargonium
x hortorum Stecklingen unter den Einflüssen der Jahreszeit der Mutterpflanzenkultur, dem
Mutterpflanzenalter, einer Kühllagerung der Stecklinge (variable Temperaturführung für 4
Tage ), als auch des Beitrages der aktuellen Photosynthese der Stecklinge in weiterer
Abhängigkeit von den Bewurzelungsbedingungen (Gewächshaus, Klimakammer: 100 µmol
-2 -1m s ). Untersucht wurden die Kohlenhydratkonzentrationen in den Blättern und in der
Sprossbasis, Chlorophyllfluoreszenzparameter, Chlorophyllqualität und –quantität sowie die
Nettophotosyntheserate der Stecklinge während der Bewurzelung.
Die Konzentrationen der Kohlenhydrate in den Stecklingsblättern zum Erntetermin wurden
nur geringfügig durch die Jahreszeit beeinflusst, durch die anschließende Kühllagerung
jedoch signifikant verringert. Stärke konnte bereits nach einem Tag Kältelagerung nur noch in
Spuren nachgewiesen werden. Der Kohlenhydratgehalt der Sprossbasis zum Zeitpunkt der
Ernte war im Sommer höher als im Frühling und Winter, was in erster Linie in einem höheren
Stärkegehalt begründet war. Die Kühllagerung führte nur im Frühling und Winter zu einer
signifikanten Reduzierung der Kohlenhydrate der Sprossbasis. Der nicht-photochemische
Quenching-koeffizient (qN) der Chlorophyllfluoreszenz zum Zeitpunkt des Steckens wurde
nur geringfügig durch die Jahreszeit beeinflusst, aber durch die Kühllagerung signifikant
reduziert. Unabhängig von den Bewurzelungsbedingungen wurden diese Unterschiede jedoch
bereits innerhalb eines Tages während der Bewurzelung ausgeglichen. Mit Ausnahme der
Bewurzelung in Gewächshaus im Winter traf dies ebenfalls auf die am Tag 7 gemessenen
Kohlenhydratkonzentrationen in den Stecklingen zu. Darüber hinaus waren während der
Stecklingsbewurzelung im Frühling und Sommer qN und Kohlenhydratgehalte in der
Klimakammer signifikant niedriger als unter den Gewächshausbedingungen. Dies deutet auf
eine verminderte Photosyntheseleistung, eine dadurch verringerte Kohlenhydratsynthese und
einen nachfolgend beeinträchtigten basipetalen Kohlenhydrattransport in den Starklicht-
adaptierten Stecklinge unter den relativ niedrigen Lichtbedingungen der Klimakammer. Die
Kohlenhydratverteilung in den Blättern und in der Sprossbasis während der Bewurzelung
deutet darauf hin, dass der neu assimilierte Kohlenstoff in den Blättern vornehmlich
zwischen Saccharose und Stärke verteilt, anschließend in Richtung Sprossbasis exportiert und
dort bevorzugt in der Zuckerfraktion akkumuliert wurde.
Unabhängig von der Jahreszeit wurden für ungelagerte und gelagerte „Isabell“- Stecklinge
hoch signifikante positive Korrelationen zwischen der Saccharosekonzentration in den Blätten
bzw. dem qN zum Stecktermin und der Anzahl nachfolgend unter den
Klimakammerbedingungen gebildeten Adventivwurzeln ermittelt. Im Gewächshaus konnten
solche Korrelationen nur für den Winter gefunden werden (geringes Lichtangebot). Der nicht-
photochemische Quenching-koeffizient qN kann möglicherweise als schneller und nicht
destruktiver physico-chemischer Index zur Vorhersage der Bewurzelung verwendet werden,
wenn diese unter definierten relativ schwachen Lichtbedingungen (praxisübliche Bedingung
in Mitteleuropa) erfolgt. Mit Hilfe der mittleren Saccharosekonzentration der Blätter (Tag 1 +
Tag 7) konnte die Variabilität der Wurzelanzahl, verursacht durch die unterschiedlichen
Jahreszeiten, das Mutterpflanzenalter, die Kühllagerung und die Bewurzelungsbedingungen,
gut erklärt werden. Die Ergebnisse zeigen, dass auch unter der Bedingung hoher
Kohlenhydratgehalte der Sprossbasis zum Zeitpunkt des Steckens die Adventivwurzelbildung
von Pelargonium-Stecklingen durch die basipetale Translokation der Kohlenhydrate limitiert
wird, welche sowohl von den bereits vorhandenen Kohlenhydratreserven im Blatt als auch
von der aktuellen Photosynthese abhängt, wobei Letztere im wesentlichen dem Einfluss des
Lichtangebotes während der Bewurzelung unterliegt. Key words


English: Carbohydrates, photosynthesis, adventitious root formation

Deutsch: Kohlenhydrate, Photosynthese, Bewurzelung

CONTENTS

1 INTRODUCTION...................................................................................... 1

2 MATERIALS AND METHODS.............................................................. 7

2.1 Plant material............................................................................................. 7

2.2 Experimental design.................................................................................. 7
2.2.1 Preliminary experiments: Carbohydrate distribution................................... 7
2.2.1.1 Within the leaf ............................................................................................ 7
2.2.1.2 Validation of relation between basal 1 cm section of leaf and whole leaf.. 8
2.2.2 Experiment 1: Effect of season, stock plant age, storage and rooting
environment – cv. ‘Isabell’.......................................................................... 9
2.2.3 Experiment 2: Effect of storage temperature regimes – cv. ‘Isabell’.......... 10
2.2.4 Experiment 3: Effect of stock plant age and storage – cv. ‘Mitzou’........... 11

2.3 Experimental conditions............................................................................ 12
2.3.1 Stock plant cultivation and stock plant age.................................................. 12
2.3.2 Conditions of storage................................................................................... 13
2.3.3 rooting....14
2.3.3.1 Greenhouse................................................................................................... 14
2.3.3.2 Climate chamber.......................................................................................... 15

2.4 Chemical and Non-destructive measurements........................................ 16
2.4.1 Carbohydrate analysis.................................................................................. 16
2.4.2 Chlorophyll fluorescence measurement....................................................... 19
2.4.3 estimation................................................................................. 20
2.4.4 Stomatal gas exchange................................................................................. 20

2.5 Determination of adventitious root formation........................................ 21

2.6 Statistical analysis...................................................................................... 21
CONTENTS
3 RESULTS................................................................................................... 22

3.1 Carbohydrate distribution within leaves of freshly excised and stored
cuttings of ‘Isabell’..................................................................................... 22
3.1.1 Effect of leaf section – cv. ‘Isabell’............................................................. 22
3.1.2 Relationship between basal section and whole leaf – cv. ‘Isabell’.............. 24

3.2 Effect of season, stock plant age, storage and rooting environment on
carbohydrate distribution, photosynthetic performance and root
formation of ‘Isabell’ cuttings .................................................................. 26
3.2.1 Pre-insertion condition................................................................................. 26
3.2.1.1 Carbohydrate distribution – cv. ‘Isabell’..................................................... 26
3.2.1.2 Chlorophyll fluorescence values – cv. ‘Isabell’........................................... 35
3.2.1.3 Chlorophyll content – cv. ‘Isabell’.............................................................. 37
3.2.2 During course of propagation...................................................................... 37
3.2.2.1 37
3.2.2.2 41
3.2.2.3 Net photosynthetic rate – cv. ‘Isabell’......................................................... 41
3.2.2.4 Carbohydrate status – cv. ‘Isabell’............................................................... 42
3.2.2.5 Visual observations – cv. ‘Isabell’............................................................... 52
3.2.3 Rooting efficiency – cv. ‘Isabell’................................................................. 52
3.2.4 Relationship between pre-insertion condition and subsequent root
formation...................................................................................................... 56
3.2.4.1 Correlation between pre-insertion carbohydrates and root number – cv.
‘Isabell’........................................................................................................ 56
3.2.4.2 Correlation between pre-insertion quenching values and root number -
cv. ‘Isabell’................................................................................................... 61
3.2.5 Relationship between pre-insertion condition, performance during
propagation and subsequent root formation................................................. 65
3.2.5.1 Correlation between quenching values and root number – cv. Isabell’....... 65
3.2.5.2 Correlation between carbohydrates and root number – cv. ‘Isabell’........... 66
CONTENTS
3.3 Effect of storage temperature regimes on rooting of ‘Isabell’ cuttings
under low light conditions (climate chamber)......................................... 70
3.3.1 Carbohydrates during storage – cv. ‘Isabell’............................................... 70
3.3.2 Regression between storage temperatures and carbohydrate depletion –
cv. ‘Isabell’................................................................................................... 75
3.3.3 Chlorophyll fluorescence values – cv. ‘Isabell’........................................... 77
3.3.4 Rooting efficiency – cv. ‘Isabell’................................................................. 77

3.4 Effect of stock plant age and storage on carbohydrate distribution,
photosynthetic performance and root formation of ‘Mitzou’ cuttings
under climate chamber conditions........................................................... 78
3.4.1 Carbohydrate status – cv. ‘Mitzou’.............................................................. 78
3.4.2 Chlorophyll fluorescence values – cv. ‘Mitzou’.......................................... 84
3.4.3 Chlorophyll content – cv. ‘Mitzou’.............................................................. 85
3.4.4 Rooting efficiency – cv. ‘Mitzou’................................................................ 86
3.4.5 Relationship between pre-insertion condition, performance during
propagation and subsequent root formation – cv. ‘Mitzou’......................... 87

4 DISCUSSION............................................................................................. 88

4.1 Carbohydrate distribution within the leaves .......................................... 88
4.2 Pre-insertion condition of the cuttings as affected by season, harvest
and storage.................................................................................................. 88
4.2.1 Carbohydrate distribution............................................................................ 88
4.2.2 Chlorophyll fluorescence............................................................................. 91
4.2.3 Chlorophyll quality and quantity................................................................. 92
4.3 Post-insertion performance....................................................................... 93
4.3.1 Current photosynthetic efficiency................................................................ 93
4.3.2 Current photosynthetic performance............................................................ 96
4.3.3 Contribution towards basal stem.................................................................. 98
4.4 Rooting response........................................................................................ 103
4.4.1 Rooting response as related to pre-insertion condition................................ 103CONTENTS
4.4.2 Rooting response as related to pre-insertion condition and performance
during propagation 106
4.5 Internal quality and rooting response of the cuttings as affected by
storage temperature regimes..................................................................... 110
4.6 Predicting the rooting capacity of cuttings.............................................. 111

5 SUMMARY................................................................................................ 114

6 BIBLIOGRAPHY...................................................................................... 117

7 APPENDIX................................................................................................. 127